As known, the gas turbines of this type can be powered, according to their operating cycle, either with natural gas or synthetic gas, or on synthetic gas. The use of synthetic gas for the supply of gas turbines causes relatively high risks of auto-inflammation, when a non-controlled air and synthetic gas mixture subsists in the supply pipes.
This is the reason for which it is necessary to implement two purge phases of the portions of the supply network of the turbines by injecting an inert gas, as for example carbon dioxide or nitrogen dioxide.
For example, when they are not supplied with fuel, the turbine gas injectors must be swept by hot air from the outlet of the turbine compressor. In order to avoid any contact between hot air, whose temperature can attain 400° C., and synthetic gas, we implement a purge of the portions of pipes likely to contain synthetic gas, by injection of inert gas. It particularly consist in injecting inert gas in the portions of supply pipes located between two control valves, generally referred to by the term “cavity”, or in the collectors or distributors, generally referred to by the term “manifold” for the supply of fuel injectors or combustive combustion chamber.
It is already known, from the state of the technique, inert gas injection techniques in a gas turbine supply network.
In this regard we can refer to the document JP 2002 129 981 or JP 11 210 494 in which inert gas is injected between two supply valves of the turbine with fuel, particularly when the supply is cut off.
It is also known from the document JP 2010 065 579 to inject in a fuel supply pipe, before ignition of the turbine combustion chamber.
We can also refer to the document
US 2001/0 022 080 which also describes an inert gas injection process according to the pressure existing in a supply pipe of a turbine with fuel.
The document US 20110036092 also concerns a supply procedure of a gas turbine supply network distributor capable of implementing the purge sequences.
Moreover, the inert gas used to implement the purge phase, is provided in tanks designed in a manner as to respect a specific pressure range lying between a minimum pressure which must be greater than the pressure likely to exist in the entire supply network in order to avoid return of toxic gas and whose maximum pressure must be less than the maximum pressure acceptable for various elements constitutive of the supply network.
As shown in FIG. 1, it was observed that when the purge phase of the various portions of the supply network is implemented, the inert gas pressure provided by a storage tank upstream of the supply network falls suddenly due to the establishing of a high inert gas flow in the lines to purge and this, in spite of the presence of flow control valves, duly set, and a pressure regulation system of the inert gas tanks.
The pressure regulation system of the tank is capable of resetting the pressure, after sudden drop. However, this pressure resetting is not sufficiently reactive to satisfy the safety criteria generally imposed at the production power plants using gas turbines.
During the transitory pressure drop, the inert gas supply pressure is likely to pass below the safety protection levels based on the fuel gas pressure and hot air pressure, leading to an emergency stop of the gas turbine and consecutive loss of production.
The aim of the invention is thus to compensate for this inconvenience and, consequently, propose a purge process of the supply pipe network of a gas turbine powered with a fuel at least partly containing synthetic gas, by inert gas injection in the portions of the pipe network likely to contain fuel or hot air in order to avoid contact between fuel and hot air when the fuel supply is stopped.
According to a general characteristic of this process, inert gas is injected in the said portions of the network according to a sequence of respective injections.
The supply of the said portions of the network according to a predetermined order, i.e. by avoiding to simultaneously supply all the portions of the network, allows avoiding any inert gas pressure drop at the inlet of the gas supply network of the machine, in a manner that the inert gas supply pressure is maintained above the minimum threshold value.
According to another characteristic, inert gas is supplied to the said portions according to a supply order determined according to the configuration of the pipe network in a manner as to maintain a positive supply flow in the direction of the turbine combustion chamber.
Favorably, the purge is stopped according to a sequence depending on the order of supply.
According to another characteristic, inert gas is injected in the portions of the fuel supply pipe marked with fuel supply control valves.
Inert gas can also be injected in the portions of fuel supply pipes marked with fuel supply control valves.
Moreover inert gas can be injected in one or each collector or distributors supplying the injectors with fuel.
In implementation mode, inert gas is injected in one or each collector or distributors for supplying the turbine with combustive fuel.
According to another characteristic of the process as per the invention, inert gas is injected at a pressure higher than the fuel gas pressure.
It is to be noted that additionally inert gas is injected at a pressure higher than the pressure of hot air present in a turbine compressor.
In implementation mode, the said portions are supplied with inert gas according to a supply order determined as per the configuration of the pipe network in a manner as to maintaining a positive supply flow in the direction of the turbine combustion chamber.
Moreover, it must be noted that inert gas is for example nitrogen or carbon dioxide.